Active materials and corrosion layers in positive plates of nonantimonial lead/acid batteries, at different stages of charge/discharge cycling, have been characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). In the initial stages of cycling, it has been found that the observed overcharging of cells is responsible for the formation of an underlayer of PbO in the grid corrosion layer, and this blocks the transfer of charge to the current collecting grid, causing rapid capacity loss. In the later stages of cycling at a ratio of capacities for charge and discharge (i.e., C/D) of close to unity, the grid corrosion layer does not possess an underlayer of PbO; however, the active material becomes progressively enriched with respect to insulating lead sulfate. It is suggested that initial overcharging is symbolic of grid corrosion as the rate of gassing side reactions is kept to a minimum by restricting the top-of-charge-voltage (TOCV) to 2.55 V, while sulfation of active material occurring at C/D values of about unity is probably attributable to stratification of the electrolyte and its concomitant effect on sulfation of active material.